The present invention generally relates to sensing devices, and more particularly to absolute position sensing devices with a high sensing resolution.
Position sensors are used in a variety of devices to allow electrical systems to sense the motion or position of moving objects and components. Types of position sensors include, for example, analog potentiometers, digital encoders and capacity sensors, among other types of position sensors. These types of sensors may be used to track motion and position over a wide range of distances, and may have a similarly wide range of sensing resolutions. A position sensor""s sensing resolution determines the incremental amount of motion or displacement detectable by the sensor. For example, a higher sensing resolution allows the censor to detect smaller increments of movement.
In some instances when tracking the movement and position of a component, it may be necessary or desirable to have a very high sensing resolution relative to the distance over which the position must be tracked. For example, one possible use of high resolution position sensors may be seen in the U.S. Pat. No. 5,557,596 to Gibson et al., in which an ultra high-density storage device is described and claimed. The ultra high-density storage device of Gibson et al. uses field emitters which generate electron beam currents. The electron beam currents write information onto storage areas of a storage medium. The storage medium is positioned on a movable rotor. The rotor is moved by one or more micromovers with respect to the field emitters so that the emitters can write and access information at a number of storage areas on the storage medium.
To properly control the micromovers for high-resolution devices such as the high-density storage device of Gibson et al., a position sensor capable of accurately indicating the relative position of the rotor with respect to the emitter wafer is needed. The sensor must indicate the position of the rotor over the entire stroke of the micromover (perhaps on the order of 50 to 100 xcexcm), yet supply resolution down to a small percentage of a track width (perhaps on the order of 0.01 to 0.10 xcexcm).
A method for determining the position of a rotor with respect to a stator is described herein. The method includes generating offset N and Q signals when the rotor moves with respect to the stator and sampling the N and Q signals at a predetermined time interval. A section of a polar plot in which the N and Q signal sample lies is determined and compared to the section of a polar plot in which a previous N and Q signal sample lies. A long range rotor position is calculated by maintaining a count of the change of sections from previous N and Q signal samples. A sub-section rotor position for the N and Q signal sample is calculated and combined with the long range rotor position to create a linear position signal.